1. Field of the Invention
This invention relates to silicone emulsions which yield an elastomer upon removal of the water at ambient conditions
2. Background Information
Silicone emulsions which yield an elastomer upon removal of the water are known in the art. U.S. Pat. No. 3,355,406, issued Nov. 28, 1967, teaches silicone rubber latexes reinforced by adding silsesquioxane. In example 19, a composition of hydroxyl endblocked polydiorganosiloxane, silsesquioxane, methylhydrogenpolysiloxane, and dibutyltin dilaurate is taught. Upon evaporation of the water from a film of the latex, a silicone rubber film was left.
Silicone paper release coatings are taught in U.S. Pat. No. 4,190,688, issued Feb. 26, 1980. The emulsion comprises a vinyl-containing polydiorganosiloxane having hydroxyl endblocking, a hydride cross-linking agent, water, and an emulsifying agent. The composition can be cured either with a tin salt of a carboxylic acid or it can be cured with a platinum complex catalyst.
U.S. Pat. No. 4,221,688, issued Sept. 9, 1980, teaches a silicone emulsion having a dispersed phase of an anionically stabilized hydroxylated polydiorganosiloxane and a colloidal silica. In order to form a cured elastomer in a reasonable time, a tin catalyst is also present. Experience has now shown that such a system continues to cure in the emulsion and after drying, so the properties of the elastomer formed are dependent upon the age of the emulsion and the age of the dried film. The additional requirement of a pH of greater than 9 is also undesirable in many cases.
A latex of crosslinked silicone is prepared in U.S. Pat. No. 4,248,751, issued Feb. 3, 1981, by emulsifying a vinyl endblocked polydiorganosiloxane and an organosilicon compound having silicon-bonded hydrogen atoms with water and a surfactant, adding platinum catalyst, and then heating the emulsion. Colloidal silica can be added to the emulsion to provide a tougher product.
U.S. Pat. No. 4,273,634, issued June 16, 1981, teaches an emulsion comprising a continuous water phase and a dispersed phase of crosslinked silicone. The silicone phase is the product of radical produced crosslinking of hydroxyl endblocked polydiorganosiloxane which was crosslinked after it had been dispersed in water.
U.S. Pat. Nos. 4,568,718, issued Feb. 4, 1986, and 4,584,341, issued Apr. 22, 1986, teach latexes of crosslinked polydiorganosiloxane. The latex is prepared by homogenizing a mixture of hydroxyl endblocked polydiorganosiloxane, surface active anionic catalyst, and alkoxy silicon compound, then polymerizing to form a crosslinked polymer. The polymer can be reinforced by adding colloidal silica to the emulsion. An elastomer is formed when the latex is dried.